(i) Field of the Invention
The present invention relates to a controller of a hybrid electric vehicle having an engine-driven power generator.
(ii) Description of the Prior Art
An electric vehicle has become prominent in view of low pollution in recent years. However, because it is essential for the electric vehicle to have a battery as its energy source and the battery has a considerable volume and weight, it is impossible to greatly increase the battery capacity. Therefore, a hybrid electric vehicle having an engine-driven power generator is proposed to charge the battery. The hybrid electric vehicle operates the engine-driven power generator when the battery charge quantity decreases in order to recover the battery charge state. Therefore, it is possible to increase the running distance per unit charge without greatly increasing the battery capacity. Moreover, engine driving for power generation can be carried out with a small exhaust quantity of pollutant because load fluctuation of the engine driving for power generation is smaller than that of engine driving for running. This type of hybrid electric vehicle is disclosed in the official gazette of, for example, Japanese Patent Laid-Open No. 21210/1975.
For an existing hybrid electric vehicle, however, it is necessary to increase the electric power quantity generated by an engine so as to correspond to the discharge quantity at this time in order to prevent a battery from deteriorating due to over discharge during high-speed running. Therefore, the existing hybrid electric vehicle has a problem that the engine and power generator are increased in size and weight and it is difficult to mount them in a vehicle.
As the hybrid electric vehicle, a series hybrid electric vehicle using its engine only to drive its power generator is generally used. However, a parallel hybrid electric vehicle capable of using the driving force generated by the engine to run the vehicle is also known. The parallel hybrid electric vehicle makes it possible to achieve running at a high energy efficiency. However, the parallel hybrid electric vehicle has a problem that the exhaust quantity of pollutant increases because the engine load fluctuates.